The invention relates to “active implantable medical devices” as defined by the Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European communities, particularly to devices that continuously monitor heart rhythm and deliver if necessary stimulation, resynchronization and/or defibrillation electrical pulses to the heart in case of arrhythmia detected by the device.
The invention relates especially, but is not limited, to those devices which are in the form of an autonomous capsule for implantation in a heart chamber (atrium or ventricle, right or left).
The capsules are free of any mechanical connection to an implantable (such as a housing of the stimulation pulse generator) or non-implantable (external device such as programmer or monitoring device for patient remote monitoring) main device, and for this reason are called “leadless capsules” to distinguish them from electrodes or sensors disposed at the distal end of a conventional probe (lead), which is traversed throughout its length by one or more conductors galvanically connecting the electrode or sensor to a generator connected to an opposite, proximal end of the lead. However the autonomous nature of the capsule is not inherently a necessary feature of the invention.
The invention is applicable to the explantation of such capsules provided at their distal end with an anchoring member such as an helical screw, axially extending from the body of the capsule and designed to penetrate into the cardiac tissue by screwing during implantation at the selected site. The explantation is particularly delicate because it is necessary, first, to catch the body of the capsule via an explantation accessory and, second, to exert on the body a rotation torque to detach it from the implantation site wherein it was maintained by the anchoring screw. This torque should be large enough to overcome resistance and adhesions resulting from fibrous tissue that are locally formed.
Explantation accessories, designated as “lassos” or snares, are commonly used to capture and remove medical equipment such as a lead body, defective catheters, guides, etc., out of the heart chambers and venous system. These lassos consist of a flexible wire terminated at its distal end by a deformable loop of shape memory metal, the loop extending in the free state in a plane generally perpendicular to the metal wire that supports it. The metal wire is introduced into the distal orifice of a catheter, crossing therethrough to emerge proximally. The tension of the wire from the proximal end of the catheter has the effect, at the other end, to draw the loop by making it gradually enter the catheter wherein it will be housed.
The operation consists in introducing the catheter into the patient's body, with the loop fully folded in the distal end region. The loop is then deployed from the catheter by pushing the wire from the proximal end. Due of the shape memory of the metal, the loop then resumes its lasso shape inclined relative to the direction of the wire and of the catheter. The lasso can be oriented at will to capture the element to be extracted. Pulling on the wire then makes it possible to partially enter the loop in the catheter, which has the effect of reducing its size and ensuring clamping of the element to be removed.
WO 2012/082755 A1 describes a leadless capsule explantation accessory based on this principle, which implements a catheter with a lasso mechanism to permit capture of the capsule at the distal end of the catheter, a docking member being possibly coupled to the proximal end of the capsule. When the loop of the lasso is tightened, the catheter docking member is coupled to the capsule, allowing the transmission of an unscrewing and removal torque of the capsule, which remains fixed to the docking member.
The drawback of this type of device is the issue that, when handling the lasso, it could trap valve tissue or filaments present in the vicinity of the capture, especially when tightening the loop lasso. Tissues, and in particular the valve tissues, captured in the same time as the capsule, could be damaged at the time of extraction.
The tissue capture risk is increased by the lack of visibility during the operation, which is performed by a practitioner under an image intensifier coupled with X-ray equipment, remote from the explantation site (typically with a femoral access for introduction of the catheter intended to reach the right ventricular cavity). The risk is increased also by the difficulty in controlling the fixation of the lasso to the capsule before removing the assembly.